Such a heat exchanger generally comprises at least one water box mounted at one end of a bundle of tubes through which a fluid flows, for example the cooling fluid of the internal combustion engine in a motor vehicle. It is conventional to provide an orifice through the wall of the water box and to close said orifice by means of a stopper including an operating head, an intermediate portion having a sealing ring mounted thereon, and a tail formed with radial ribs which constitute slopes that co-operate with complementary slopes on the edge of the orifice in the water box to enable the stopper to be mounted in the orifice and held in a sealed closure position therein.
The present Assignee's published French patent application No. 83 12 211, now French Pat. No. 2,549,532 describes a device of this type for a water box molded in plastic material in which the slopes at the orifice through the wall of the water box are plane and extend in the same plane as the orifice itself, thereby facilitating unmolding. The complementary slopes formed on the tail of the stopper are L-shaped and comprise a first plane portion perpendicular to the axis of the stopper tail and a second plane portion parallel to said axis and constituting an abutment which determines the closure position of the stopper in the orifice.
In order to bleed or drain the heat exchanger, the stopper is rotated, e.g. through one-quarter of a turn from said closure position. The stopper must then be drawn outwardly in translation along its axis in order to enable said bleeding or draining of the heat exchanger to take place. This last operation is by no means obvious to an uninstructed person. Further, the sealing ring provided around the intermediate portion of the stopper bears against a cylindrical surface of the water box wall formed around the orifice, so that friction between said sealing ring and said cylindrical surface opposes easy extraction of the stopper. If a person persists in attempting to turn the stopper about its axis instead of withdrawing it along its axis, the stopper may be damaged.
The aim of the present invention is to provide a device of the type described in the Assignee's prior patent, while avoiding the above-specified drawbacks.